1. Field of the Invention
The invention is directed to an adjustable damping valve.
2. Related Art
FIG. 1 shows as prior art an adjustable damping valve 1 for a vibration damper in a variant that can be fastened to a piston rod. The damping valve 1 comprises a housing 3 with a valve seat ring 5 which can be moved axially within limits. An axially movable valve body 9 is preloaded by a valve spring 11 in the closing direction on a valve seat surface 7 of the valve seat ring. The valve seat ring 5 is supported by its conical valve surface on a valve seat surface 12 on the housing side. The valve body 9 can slide axially in a stepped opening 13 of the housing and itself has an outer contour which is stepped 15 relative to a guide sleeve 17. At least one eccentric connection opening 19 connects an underside facing in direction of the valve seat surface 7 to a rear side of the valve body 9. Therefore, with an incident flow to the valve body through the valve seat ring 5, two pressure-loaded surfaces are available at the valve body 9. One pressure-loaded surface AÖD acting in the lifting direction on the valve body 9 is defined by the inner diameter of the contact surface of the valve body 9 on the valve seat surface 7. The valve ring 5 remains in the indicated position because the surface AÖD is greater than the diameter of the valve seat surface 12. A pressure force acts in the closing direction of the valve body 9 by way of the projected surface ASchlieβD with the diameter of the guide sleeve 17 and a pressure pÖ of the underside. The rear side of the valve body is acted upon by damping medium to achieve pressure equalization and accordingly so as to move the valve body using less energy. The pressure-loaded surface AÖD is slightly larger than surface ASchlieβD, wherein manufacturing deviations are taken into account in calculating the difference so that the valve body can lift more easily in a defined manner with the spring force in full effect.
A magnetic force acting counter to the spring force of the valve spring 11 can be introduced by means of a coil 21 in combination with an armature sleeve 23. With an incident flow to the valve body 9 through a through-opening 25 of the valve seat ring 5, the greatest damping force is achieved when the magnetic force equals zero and the full spring force of the valve spring 11 is available in the closing direction of the valve body 9. A particularly large opening pressure pÖ is then required at the underside of the valve body 9 for the lifting movement of the valve body 9.
When the coil 21 is energized to the maximum extent, the magnetic force at least partially compensates for the spring force of the valve spring 11 so that a lifting movement of the valve body 9 takes place already at an appreciably lower pressure pÖ at the surface AÖD.
For a second incident flow direction, the valve body 9 has a second annular surface AÖZ to which pressure is applied in the opening direction and which is determined by the outer diameter in the area of a step 27 of the valve body 9 and the outer diameter of the contact surface of the valve ring 5 on the housing-side valve seat surface 12. With incident flow to the valve body 9 and valve seat ring 5 through at least one radial opening 29 in the housing 3, a lifting force acts on the annular surface AÖZ against the spring force of the valve spring 11 and an annular pressure-loaded surface ASchlieβZ at the shoulder 15 of the valve body 9 which is supplied with pressure medium via a parallel channel 31 and acts in closing direction. Damping medium can flow into radial channels 37 of the valve body 9 through channel 31 via an annulus 33 between the shoulder 15 and the step 35 in the housing 3 and can act on a valve plunger 39 which is preloaded by the valve spring 11. The pressure on the valve plunger 39 acts as an opening force on the valve plunger 39 and as an additional closing force for the valve body 9 so that the valve plunger can lift easily from the valve body as the case may be. When the coil 21 is energized, the valve plunger 39 lifts slightly from the valve body 9 so that an annular gap is formed. However, the cross section of the at least one connection opening 19 is appreciably larger than this annular gap so that no pressure which could exert a closing force on the valve body 9 can build on the rear side of the valve body.
In the through-pass position of the damping valve, the damping medium can flow via the radial channels 29 through the gap between the valve seat ring 5 and the valve seat surface 12 on the housing side. As can be seen from the description, the pressure-loaded surfaces AÖ and ASchlieβ are independent from one another, i.e., if surface ASchlieβZ, for example, are enlarged at the shoulder 15, it would have no effect on the size of the pressure-loaded surface AÖD.
The ratio of maximum damping force to minimum damping force is referred to as a spread of the damping force characteristics of the adjustable damping valve. It has turned out in practice that the characteristic spread should be greater than before. A very simple possibility would be to use an appreciably higher preloading of the valve spring. However, a valve spring design of this type would also result in an increase in the required opening force in case of incident flow to the valve body from the radially outer side. But this operating behavior is undesirable.